The present invention generally relates to write-in and read-out control apparatuses for controlling write-in and read-out of picture element data with respect to a memory circuit, and more particularly to a write-in and read-out control apparatus which is designed to write picture element data which are reproduced from an information signal recording medium and correspond to one frame into a frame memory with the picture element data unchanged, write picture element data which are reproduced from the information signal recording medium and correspond to one field into the frame memory with the picture element data duplicated, and read the picture element data which amount to one frame out from the frame memory in a predetermined sequence, so as to reproduce a still picture.
Generally, there is a known reproducing apparatus which reproduces a digital video signal recorded on tracks which are formed on a rotary recording medium (hereinafter simply referred to as a disc) as variations in rows of intermittent pits. The digital video signal is obtained by subjecting a video signal to a digital pulse modulation such as a pulse code modulation (PCM). As systems for reproducing the recorded digital video signal from such a disc, there is a system which reproduces the recorded signal in response to variations in the intensity of light reflected from or transmitted through the disc according to the variations in the pits formed on the disc, and a system which reproduces the recorded signal in response to variations in the electrostatic capacitance formed between a reproducing stylus and the disc according to the variations in the pits formed on the disc.
If the conventional digital video signal reproducing apparatus of the above type is designed to time-sequentially transmit a plurality of still picture information which are recorded on the disc, two frame memories are provided in the reproducing apparatus, for example. In such a reproducing apparatus, still picture information related to one or less frames are alternately written into these two frame memories. When one of the frame memories is writing therein a reproduced digital video signal, a reproduced digital video signal is read out from the other frame memory. The signal read out from the frame memory is successively passed through a digital-to-analog converter and an encoder, and then supplied to a television receiver which reproduces the signal as a picture.
The digital video signal which is related to the still picture and is recorded on the disc described above, comprises picture element data corresponding to one frame or picture element data corresponding to one field. The picture element data corresponding to one frame, consists of (114.times.4) picture element data related to the luminance signal, 114 picture element data related to the color difference signal (R-Y), and 114 picture element data related to the color difference signal (B-Y), which are respectively arranged in the scanning direction (horizontal direction of the picture), for example, and 525 picture element data related to the luminance signal, 525 picture element data related to the color difference signal (R-Y), and 525 picture element data related to the color difference signal (B-Y), which are respectively arranged in the vertical direction of the picture, for example.
On the other hand, if picture element data related to only one of the fields between a first (odd) field and a second (even) field are transmitted as the picture element data corresponding to one field, various problems were introduced. That is, compared to a reproduced still picture which is obtained according to the picture element data corresponding to one frame, the vertical resolution of a reproduced still picture which is obtained according to the picture element data corresponding to one field was poor. Moreover, the aliasing noise increased, and jitter was generated in the vertical direction. Thus, a novel information signal recording medium was proposed in a U.S. patent application Ser. No. 537,529, filed Sept. 30, 1983 and entitled "INFORMATION SIGNAL RECORDING MEDIUM AND REPRODUCING APPARATUS THEREFOR" in which the assignee is the same as the assignee of the present application. Picture element data which amount to one field and include some picture element data related to the first field and some picture element data related to the second field, are recorded on this proposed information signal recording medium. Accordingly, the picture element data which are reproduced from this proposed information signal recording medium may correspond to one frame, or amount to a total of one field in which picture element data related to 1/2 the first field and picture element data related to 1/2 the second field coexist.
The conventional frame memory in the reproducing apparatus described before, was designed to write in the reproduced picture element data in the sequence the picture element data were reproduced, regardless of whether the picture element data corresponded to one frame or one field. Thus, if the reproduced picture element data were picture element data corresponding to one frame, the reproduced picture element data were written into the frame memory to occupy its full memory capacity, and the stored picture element data were read out from the frame memory, the picture element data corresponding to one frame were reproduced so that all of the picture element data related to the second field were sequentially reproduced continuously after all of the picture element data related to the first field were sequentially reproduced. Hence, by repeating an operation in which the picture element data are read out from the frame memory with a field sequence which is the same as the field sequence with which the picture element data were written into the frame memory, it was possible to reproduce a still picture in a sequence which was in accordance with the field sequence of the standard television system.
However, when the reproduced picture element data amounted to a total of one field in which the picture element data related to 1/2 the first field and the picture element data related to 1/2 the second field coexisted, such reproduced picture element data amounting to one field were successively written into the frame memory in the reproduced sequence to occupy 1/2 its memory capacity. In this case, in order to reproduce one still picture by reading out the stored picture element data from the frame memory, it was necessary to repeatedly read out the stored picture element data so that the picture element data which were read out amounted to a total of one frame. Consequently, the stored picture element data amounting to one field, were read out from the frame memory twice. However, if the stored picture element amounting to one field were simply read out from the frame memory twice, it was impossible to reduce the noise generated in the reproduced picture due to causes such as the aliasing noise and the deterioration in the vertical resolution. Therefore, it became necessary to make the read-out addresses of the stored picture element which amount to one field different during reproduction of the first field and during reproduction of the second field, so that the picture element data related to the first field and the picture element data related to the second field are alternately arranged and displayed on each of the scanning lines during the reproducing periods of the first and second fields, and so that the combinations of the arranged picture element data are different between the reproducing period of the first field and the reproducing period of the second field.
Accordingly, there was a problem in the conventional apparatus, in that the read-out sequence with which the stored picture element data are read out from the frame memory was different according whether the stored picture element data corresponded to one frame or to one field. The number of picture element data differs according to the size of the displaying area with respect to the total display area of the picture. In the present specification, the transmission of all of the picture element data which are related to the displaying area within the total display area of the picture, will be referred to as a "frame-transmission". On the other hand, the transmission of half the picture element data which are related to the displaying area within the total display area of the picture, will be referred to as a "field-transmission". Hence, if the displaying area is equal to the total display area of the picture, the number of picture element data will amount to one frame in the case of frame-transmission, and the number of picture element data will amount to one field in the case of field-transmission. A special type of field-transmission in which half the total picture element data which are related to the displaying area are made up from picture element data related to the first field, and half the total picture element data which are related to the displaying area are made up from picture element data related to the second field, for example, will be particularly referred to as a "zigzag-transmission". Thus, if the displaying area is equal to the total display area of the picture in the case of the zigzag-transmission, the picture element data related to 1/2 the first field and the picture element data related to 1/2 the second field coexist to make up the picture element data which amount to one field.
According to the contents of the picture, there are cases where it is desirable to compose a still picture which is determined by the picture element data of frame-transmission and a still picture which is determined by the picture element data of field-transmission, to display these two still pictures in one picture. In such cases, the picture element data of frame-transmission and the picture element data of field-transmission which amount to a total of one frame, were written into a single frame memory, in a state where the picture element data of frame-transmission and the picture element data of field-transmission coexisted. Especially when displaying the picture which is determined by the picture element data of the field-transmission on a small display area within the still picture which is determined by the picture element data of frame-transmission, it was possible to move the picture which is determined by the picture element data of field-transmission and is displayed on the small display area, because the transmission period of the picture element data of field-transmission was shorter than the transmission period which was required to rransmit picture element data amounting to one field due to the small display area these picture element data of field-transmission cover. Therefore, it was possible to display a so-called partially moving picture.
However, as described previously, the read-out sequences with which the picture element data of frame-transmission and the picture element data of field-transmission were read out from the frame memory, were different in the conventional apparatus. Moreover, when the picture element data of frame-transmission and the picture element data of field-transmission were written into a single frame memory so that the picture element data of frame-transmission and the picture element data of field-transmission coexisted, it was impossible to discriminate which address region of the frame memory actually stored the picture element data of field-transmission. Therefore, there was a disadvantage in that the stored picture element data could not be read out from the frame memory in a particular read-out sequence which was intended for particular picture element data.